For many years, a wide variety of tooth replacement systems have been offered on the market under the terms tooth implant or dental implant, and some of them have been used with great success. The terms tooth implant or dental implant generally stand for the tooth replacement per se and should not be confused with the actual implant body which, as tooth root replacement, is correctly designated as implant. In the text that follows, the terms tooth implant and implant body or implant are clearly distinguished, with the tooth implant designating the tooth replacement, which comprises the implant body for anchoring in the jaw bone. Two-part and three-part tooth implants predominate on the market, and the three-part tooth implants for replacement of an individual tooth generally consist of an endosseous implant or implant body, an abutment (also called connection part or implant post), and a crown, a bridge or another prosthesis. The abutment allows the dentist to orient the crown in relation to the implant, such that the exact position of the crown in the dental arch is not solely dependent on the setting of the implant body. The setting and the position of the implant is often determined by the particular anatomical situation in the patient's jaw. The setting of the crown can be corrected by means of suitably shaped or adjustable abutments or by working the abutment after insertion.
The choice of materials for the implant is greatly limited by stringent requirements in respect of biocompatibility and of the mechanical properties of the implant. In the last few decades, titanium in particular has become the preferred material, because it has a modulus of elasticity similar to the jaw bone and has excellent biocompatibility.
However, a disadvantage of the implants and abutments made of titanium lies in their dark colour. In the event of the gum and bone receding, the dark metal parts may become visible or show through especially in the area of the front teeth, which is extremely undesirable for cosmetic reasons. In recent years, therefore, ceramics, e.g. zirconium oxide ceramic, have attracted increasing interest as an alternative material.
Critics argue that the high modulus of elasticity of implants made from zirconium oxide ceramic leads to deep-seated fractures of the implant bodies and that their lesser degree of osseointegration compared to titanium may lead to extensive inflammation that breaks up the bone. Tooth implants made from titanium are in turn thought to trigger negative reactions through metal intoxication.
Customary implant shapes include blade, needle, screw, cylinder and cone implants, which are each used for different indications. These indications are defined by the amount of available bone, the quality of the bone and the functional goal. In principle, it is possible to use subperiosteal and endosseous implants, although in practice it is almost exclusively endosseous implants that are used at present, of the types with blade systems, screw systems or cylinder systems. Commonly used endosseous implants have a substantially cylindrical structure and are screwed or hammered into a bore in the jaw bone or directly into the jaw bone. At the coronal end, the implants are provided with an open blind bore for receiving the abutment. Since the abutment for receiving the crown or a bridge protrudes through the gum into the oral cavity and is not fully enclosed by the gum, such tooth implants are referred to as semi-open. In the semi-open implants, the crown, which is in most cases made from conventional dental ceramic and/or metal, is adhesively bonded or cemented onto the abutment or the one-piece implant/abutment structure or is secured thereon by mechanical means. In the case of closed subgingival systems, by contrast, the implant is embedded as far as the level of the alveolar crest, and the mucoperiosteal cover is sewn over the implant. Once the implant has become incorporated, a second operation is needed to be able to apply the abutment and the desired bridge, crown or other prosthesis thereon. A disadvantage of all systems in which the prosthesis is adhesively bonded onto the abutment is that it is difficult to remove the residues of adhesive or of cement that emerge in the transition area between crown and abutment and/or implant during adhesive bonding.
A two-part, open transgingival system is offered by Institut-Straumann AG, Waldenburg, Switzerland, under the name ITI DENTAL IMPLANT SYSTEM. The anchoring part or implant, which is implanted through the gum, and also the associated attachment parts are in this case made of pure titanium. EP 0879024 B1 discloses a similar system in which a solid conical abutment is screwed into the implant. The receiving opening of the implant accordingly also has a conical shape. Such a conical shape is favoured by dentists since it simplifies the implantation, in particular also the taking of impressions and the production of master models. The conical connection between implant and abutment places high demands on the accuracy of fit of the structural parts, since said connection involves both a force fit and also a form fit. Such cone connections can at present be achieved with acceptable failure rates only in titanium implants having sufficiently congruent cone surfaces.
Since the dental implants have to take up considerable alternating loads during mastication, even the very slightest micromobility between the screwed structural parts leads to abrasion and wear.
It is known that the two-part systems composed of implant and abutment permit good adaptation to the geometric conditions arising in different indications. However, since the large number of components involved is regarded in principle as being disadvantageous in respect of the mechanical stability of the overall system, and since every further connection represents a possible site of attack for periodontitis or gingivitis through cleft formation, document DE 10159683, also from Straumann, proposes a one-part dental implant made of a zirconium oxide ceramic, as is known from U.S. Pat. No. 6,165,925. The implant for anchoring in the bone and the abutment for receiving a crown or bridge to be applied are made of a material based on zirconium oxide, in which case good osseointegration is achieved by special treatment of the surface with a maximum depth of roughness in the range of between 4 and 20 μm in the area of the anchoring part. The one-part implant body with integrally formed abutment has an anchoring part with a threaded portion and with a rounded lower end for screwing into the jaw bone. In a preferred embodiment, the upper end of the anchoring part merges via a slightly outwardly conically widened portion into an structural part that is formed integrally therewith and that extends in the continuation of the longitudinal axis of the threaded portion. The structural part has a frustoconical or conical shape and is provided with a flattening on one side. On the side directed towards the flattening, an axially extending groove formed in the outer surface extends downwards from the upper end face of the structural part and ends in a conical portion, which forms the attachment to the cone portion of the anchoring part. The flattening, in conjunction with the groove lying opposite it, serves for the form-fit engagement of a screwing tool, which has a correspondingly adapted socket. A disadvantage of this system is that at least the abutment has to be reworked after insertion into the mouth of the patient.
WO 2006/084346 A1 from Medin Tech discloses an implant system with an abutment made of a non-metallic material, which system comprises an implant and a prosthesis support, which in turn comprises an abutment and a collar element. Important features of the implant system are that the parts of the implant system are pushed linearly into one another and adhesively bonded to one another. Between a substantially cylindrical base post and a head part, the abutment has a cylindrical neck part with a lower projection which is designed as a polygon and serves for the radial positioning of the abutment in a corresponding recess in the shoulder of the implant. Triangular, pentagonal or heptagonal projections are described as being preferred and interact with corresponding triangular, pentagonal or heptagonal recesses in the implant shoulder and permit positioning of the abutment in three, five or seven different radial angle positions about the longitudinal axis of the implant. The central bore in the implant for receiving the base post is provided with an inner thread, which allows a screw cap or a spacer to be screwed in during the healing process. After the healing process, a collar element is pushed over the neck area of the abutment, and the base post is adhesively bonded into the threaded bore of the implant. The collar element arranged between implant and abutment must take up a considerable share of the mastication forces and, with its convex outer face, represents the surface of contact with respect to the surrounding gum. A central and continuous axial channel is arranged in the abutment to allow the adhesive to flow off. WO 2006/084346 A1 lists a whole series of ceramic and composite materials that are suitable for production of the abutment. A disadvantage of this system lies in the considerable technical effort involved in producing the central axial channel in the abutment and also in the mechanical loads and stresses to which the abutment is thereby exposed. The abutment, or the positioning element of the abutment, must therefore either be made of a material that withstands high mechanical stresses or, as has been mentioned above, must be suitably dimensioned. A further disadvantage is that the implant cannot be produced from ceramic material, with the result that a purely ceramic system composed of ceramic implant and ceramic abutment cannot be achieved according to the invention in WO 2006/084346 A1.
EP 1728486 A1 from Straumann discloses an implant system with an implant and an abutment, in which the abutment is provided with means for rotationally locked mounting of the abutment in the implant. A receiving opening in the implant is designed in such a way that a base portion of the abutment can be inserted substantially with a form fit and at the desired angle position into the receiving opening of the implant and is secured in this position on the implant by a separate screw. To receive the screw, the abutment is provided with a central continuous bore, such that the base area has to be designed with a very thin wall. The means that prevent twisting of the abutment and implant relative to each other consist in turn of a polygonal anti-rotation element on the abutment and of a recess that has a shape corresponding to the anti-rotation element. The system in EP 1728486 A1 does not allow the implant and abutment to be produced from ceramic at reasonable cost using known production methods and techniques.
Despite the large number of known systems for replacing individual teeth, for treating large gaps between the teeth and shortened rows of teeth and for securing bridges or prostheses, there is an increasing need among users for systems that avoid the disadvantages of the known systems.